I too find it rather pointless to compare tanks that are clearly made for different purposes. M1A2 is made with full logistics support in mind. It is not designed to be a "plug for every hole". The cons of M1A1 are that it is big, heavy and thus it is impossible to haul by most railroads and has trouble crossing most bridges, only 2 planes in US military (as far as I know) are able to lift it (C-5 and C-17), it uses lots of fuel to operate, relatively expensive, weak (or at least inadequate to resist RPG-7 with modern ammuninion) side and rear protection, shell trap just above the upper hull plate that is absolutely huge, making it vulnerable from the front arc. Pros: fire control system is very accurate (not very fast though), supporting electronics (diagnostics, vision, communication), crew comfort (it is like a limo compared to t90c being merely "VW golf" class). It is fast on roads and level terrain (72 or 68, depending on the model, is the limit that is forced electronically. If the need arises, one could propel the thing to nearly 100 at the expence of engine and suspension. Don't try this at home
) Quality of assembly is also very high, and if one operates it "by the book" standards, very few things will go wrong, regular service provided.
as for T-90c... it is a different beast altogether. Most obvious cons are the assembly quality (this thing is designed to be MASS produced, not hand tailored). Cramped crew compartment is very tiring to the crew. Less accurate at extreme ranges (4km+) due to more crude electronics assistance. Communication equipment is not up to par compared to western counterparts. Weak rear protection vulnerable to hand held anti tank weapons (same problems as with all tanks probably). It has not been proper battle tested, so possible weaknesses may still emerge. Sure, they were hit by RPGs on many occasions (Dagestan comes to mind) as well as polygon tested, but that is not real combat test. It is slower on roads and level terrain. Different sources claim that it is capable of 70km/h but I suspect that this figure is in the red zone since it does not have a speed limiter. Diesel engines are also more difficult to operate at cold temperatures. Ammunition storage is a disaster waiting to happen. It is also very difficult for one crew member to substitute another in battle conditions if a need arises. As I said earlier - it is really cramped. These are just what spring to mind without going into technical details.
On the other hand, T-90c is much smaller and lighter. Small silhouette makes it a more difficult target, and easier concealed and camouflaged. Lighter also does not make it any less armored. Remember - the tank is 2/3rd of abrams in size, and therefore needs much less armor weight to achieve comparable armor values. The shell trap area is much smaller and therefore the tank is better protected from frontal long range fire. Different reports also say that it is very well armored from side attacks (although validity of these is another question since battle conditions are not described well). I seriously doubt that it can resist 120mm shell in its side, but at least it is claimed on numerous occasions to being hit by RPGs from sides and still remain operational. Rumors of T-72 and T-90 series being death trap, with ammo racks exploding after every sneeze, are also greatly exaggerated. I can not quote for T-90c performance, since as I said, it is not proper battle tested, but during siege of Grozny 20 T-72 were destroyed and only 8 casualties reported. Bear in mind that they were fired at with RPGs from tall buildings and from the top projection mostly. It is also unclear whether these casualties were suffered inside the tank, or after crew evacuated they were killed in the ensuing battle. T-72 also were not equiped with active armor during these events. Since T-90c is small and light (well... as far as MBTs go anyway) it can be transported more easily. Railroad, roads, air, sea... Take 2 and get 1 free
Also less of a bridge problem.
As I said earlier, fire control is more crude on T-90c than in western vehicles and that results in relatively poor accuracy at extreme tanges for the main gun. But it is also much faster at target acquisition and firing at medium and close ranges. It is even faster than that on Leopard 2 which was holding an unofficial crown for speed shooting (8 targets in 60 secs for Leopard 2, 9 for T-90, all in the 1-2.5 km range). Althoug this record breaking performance may be adressed with a bit of suspicion since most sources claim that the rof with standard T-90 autoloaders is around 8 rpm and it is unknown to me whether they shot on the move or stationary. 9М119М missiles and its modifications that can be loaded are also a big plus and can somewhat compensate for theoretically lower accuracy and penetration values of the main gun at long range. They provide a near 100% hit probability on targets up to 5km moving up to 70km/h while the tank moves less than 30km/h. In theory. At least these figures are claimed by producers. Nevertheless t is well beyond m256 120mm gun effective range, and even if you hit T-90 at that distance, I seriously doubt that you will penetrate. Lower weight also means less stress on suspension. T-90 series are extremely maneuvrable on rough terrain. You have probably seen them jumping all over the place on youtube or some such. Whereas this is hardly "battle recommended" it shows the potential for the chassis.
Damn... I really can go on for ages talking about different tanks, advantages and disadvantages. Long story short - these are machines built for different conditions. T-90c is more of a close range fighter. It is more crude, cheaper, lighter. You can service it with a screwdriver and a hammer. In an all out, less than ideal battle situations where intel is limited, terrain is not a 15 km salt flat, your supply lines are being targeted not by a couple of extrimists, but by tank battalions, it may prove to be much more effective. M1A2 will be hard pressed to show its full potential in this situation. It is more designed for "by the book" engagements. It needs proper supply, intel, proper workshop, mechanic with a notebook and a degree in rocket science etc... Then and only then it will shine, being able to use its advantages in electronics, communication, targeting and so forth.